Method of performing an image-adaptive tone mapping and display device employing the same

ABSTRACT

A method of performing an image-adaptive tone-mapping for a display device including performing a first tone-mapping on an image frame by applying a first tone-mapping function to respective non-target display blocks, and performing a second tone-mapping on the image frame by applying a second tone-mapping function obtained by applying a local weighted value to the first tone-mapping function to respective target display blocks.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2018-0027546, filed on Mar. 8, 2018, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND Field

Exemplary embodiments of the invention relate generally to a displaydevice and, more specifically, to a method of performing animage-adaptive tone mapping that improves a contrast ratio of an imageframe by performing a tone mapping on the image frame and a displaydevice that employs the method of performing the image-adaptive tonemapping.

Discussion of the Background

Recently, a display device enhances an image quality by improving acontrast ratio of an image frame by performing a tone mapping on theimage frame. For example, the display device may perform the tonemapping on the image frame by converting an RGB signal corresponding tothe image frame to be displayed on a display panel into an YCbCr signal,by converting the YCbCr signal into an Y′Cb′Cr′ signal based on a tonemapping function (or referred to as a tone mapping curve), by convertingthe Y′Cb′Cr′ signal into an R′G′B′ signal, and by displaying the imageframe based on the R′G′B′ signal. Generally, the tone mapping may beclassified into a global tone mapping which performs the tone mapping byapplying the same tone mapping function to all pixels and a local tonemapping which performs the tone mapping by applying respective tonemapping functions to respective pixels. Here, the global tone mappinghas disadvantages in that the global tone mapping cannot properlyreflect characteristics of a specific region (e.g., a low-grayscaleregion) of the image frame because the same tone mapping function isapplied to all pixels. On the other hand, the local tone mapping hasdisadvantages in that the local tone mapping cannot be performed inreal-time because an excessively large amount of computation is requiredfor performing the tone mapping as respective tone mapping functions areapplied to respective pixels. Thus, an image-adaptive tone mapping inwhich the local tone mapping complements the global tone mapping hasbeen suggested. However, a conventional image-adaptive tone mapping hasdisadvantages in that an implementation and a real-time processing aredifficult because the conventional image-adaptive tone mapping performsthe local tone mapping, which complements the global tone mapping in acomplicated way.

The above information disclosed in this Background section is only forunderstanding of the background of the inventive concepts, and,therefore, it may contain information that does not constitute priorart.

SUMMARY

Exemplary embodiments provide a method of performing an image-adaptivetone mapping that can perform a local tone mapping which complements aglobal tone mapping in a simple way.

Exemplary embodiments also provide a display device by employing themethod of performing the image-adaptive tone mapping that can perform animage-adaptive tone mapping in real-time while easily implementing theimage-adaptive tone mapping.

Additional features of the inventive concepts will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the inventive concepts.

An exemplary embodiment of the invention provides a method of performingan image-adaptive tone mapping including calculating an entire-grayscaleluminance average, a low-grayscale luminance average, and ahigh-grayscale luminance average of an image frame to be displayed on adisplay panel by analyzing a data signal corresponding to the imageframe; determining a first tone mapping function to be applied to theimage frame based on the entire-grayscale luminance average, thelow-grayscale luminance average, and the high-grayscale luminanceaverage; dividing the display panel into a plurality of display blocksby grouping a plurality of pixels included in the display panel bylocation; classifying the display blocks into non-target display blocks,of which block luminance is greater than the low-grayscale luminanceaverage, and target display blocks, of which the block luminance is lessthan the low-grayscale luminance average; performing a first tonemapping on the image frame by applying the first tone mapping functionto each of the non-target display blocks; and performing a second tonemapping on the image frame by applying a second tone mapping function toeach of the target display blocks, the second tone mapping functionbeing obtained by applying a local weighted value to the first tonemapping function.

The first tone mapping function may be expressed by [Equation 1] below:OUTPUT1=GTM(INPUT),   [Equation 1]where GTM denotes the first tone mapping function, INPUT denotes aluminance signal which is extracted from the data signal, and OUTPUT1denotes a first output luminance signal which is obtained by performingthe first tone mapping on the luminance signal.

In exemplary embodiments, the second tone mapping function may beexpressed by [Equation 2] below:OUTPUT2=(1+α)×GTM(INPUT),   [Equation 2]where GTM denotes the first tone mapping function, INPUT denotes theluminance signal which is extracted from the data signal, α denotes thelocal weighted value, and OUTPUT2 denotes a second output luminancesignal which is obtained by performing the second tone mapping on theluminance signal.

The local weighted value may decrease within a predetermined weightedvalue range as a luminance ratio, which is calculated by dividing theblock luminance of the each of the target display blocks by thelow-grayscale luminance average, increases. In addition, the localweighted value may increase within the predetermined weighted valuerange as the luminance ratio decreases.

The pixels may be classified into high-grayscale luminance pixels, ofwhich pixel luminance is greater than the entire-grayscale luminanceaverage and low-grayscale luminance pixels, of which the pixel luminanceis less than the entire-grayscale luminance average. In addition, theentire-grayscale luminance average may be calculated as an average ofthe pixel luminance of all of the pixels, the low-grayscale luminanceaverage may be calculated as an average of the pixel luminance of thelow-grayscale luminance pixels, and the high-grayscale luminance averagemay be calculated as an average of the pixel luminance of thehigh-grayscale luminance pixels.

The block luminance may be calculated as an average of the pixelluminance of the pixels included in each of the display blocks.

The block luminance may be calculated as a weighted average of the pixelluminance of the pixels included in each of the display blocks.

The block luminance may be determined as a minimum grayscale amonggrayscales corresponding to the pixel luminance of the pixels includedin each of the display blocks.

Another exemplary embodiment of the invention provides a method ofperforming an image-adaptive tone mapping including calculating anentire-grayscale luminance average, a low-grayscale luminance average,and a high-grayscale luminance average of an image frame to be displayedon a display panel by analyzing a data signal corresponding to the imageframe; determining a first tone mapping function to be applied to theimage frame based on the entire-grayscale luminance average, thelow-grayscale luminance average, and the high-grayscale luminanceaverage; dividing the display panel into a plurality of display blocksby grouping a plurality of pixels included in the display panel bylocation; classifying the display blocks into non-target display blocks,of which block luminance is greater than a block luminance average of Nadjacent display blocks, where N is an integer greater than or equal to8, and target display blocks, of which the block luminance is less thanthe block luminance average; performing a first tone mapping on theimage frame by applying the first tone mapping function to each of thenon-target display blocks; and performing a second tone mapping on theimage frame by applying a second tone mapping function to each of thetarget display blocks, the second tone mapping function being obtainedby applying a local weighted value to the first tone mapping function.

In exemplary embodiments, the first tone mapping function may beexpressed by [Equation 1] below:OUTPUT1=GTM(INPUT),   [Equation 1]where GTM denotes the first tone mapping function, INPUT denotes aluminance signal which is extracted from the data signal, and OUTPUT1denotes a first output luminance signal which is obtained by performingthe first tone mapping on the luminance signal.

In exemplary embodiments, the second tone mapping function may beexpressed by [Equation 2] below:OUTPUT2=(1+α)×GTM(INPUT),   [Equation 2]where GTM denotes the first tone mapping function, INPUT denotes theluminance signal which is extracted from the data signal, a denotes thelocal weighted value, and OUTPUT2 denotes a second output luminancesignal which is obtained by performing the second tone mapping on theluminance signal.

The local weighted value may decrease within a predetermined weightedvalue range as a luminance ratio which is calculated by dividing theblock luminance of the each of the target display blocks by the blockluminance average of the N adjacent display blocks increases. Inaddition, the local weighted value may increase within the predeterminedweighted value range as the luminance ratio decreases.

The pixels may be classified into high-grayscale luminance pixels, ofwhich pixel luminance is greater than the entire-grayscale luminanceaverage and low-grayscale luminance pixels, of which the pixel luminanceis less than the entire-grayscale luminance average. In addition, theentire-grayscale luminance average may be calculated as an average ofthe pixel luminance of all of the pixels, the low-grayscale luminanceaverage may be calculated as an average of the pixel luminance of thelow-grayscale luminance pixels, and the high-grayscale luminance averagemay be calculated as an average of the pixel luminance of thehigh-grayscale luminance pixels.

The block luminance may be calculated as an average of the pixelluminance of the pixels included in each of the display blocks.

The block luminance may be calculated as a weighted average of the pixelluminance of the pixels included in each of the display blocks.

The block luminance may be determined as a minimum grayscale amonggrayscales corresponding to the pixel luminance of the pixels includedin each of the display blocks.

Another exemplary embodiment of the invention provides a display deviceincluding a display panel including a plurality of pixels, and a displaypanel driving circuit configured to drive the display panel. The displaypanel driving circuit calculates an entire-grayscale luminance average,a low-grayscale luminance average, and a high-grayscale luminanceaverage of an image frame to be displayed on the display panel byanalyzing a data signal corresponding to the image frame, determines afirst tone mapping function to be applied to the image frame based onthe entire-grayscale luminance average, the low-grayscale luminanceaverage, and the high-grayscale luminance average, divides the displaypanel into a plurality of display blocks by grouping the pixels bylocation, classifies the display blocks into non-target display blocksand target display blocks based on block luminance of each of thedisplay blocks, performs a first tone mapping on the image frame byapplying the first tone mapping function to each of the non-targetdisplay blocks, and performs a second tone mapping on the image frame byapplying a second tone mapping function to each of the target displayblocks, the second tone mapping function being obtained by applying alocal weighted value to the first tone mapping function.

The display panel driving circuit may classify the display blocks intothe non-target display blocks, of which the block luminance is greaterthan the low-grayscale luminance average and the target display blocks,of which the block luminance is less than the low-grayscale luminanceaverage.

The display panel driving circuit may classify the display blocks intothe non-target display blocks, of which the block luminance is greaterthan a block luminance average of N adjacent display blocks, where N isan integer greater than or equal to 8, and the target display blocks, ofwhich the block luminance is less than the block luminance average.

The first tone mapping function may be expressed by [Equation 1] below:OUTPUT1=GTM(INPUT),   [Equation 1]where GTM denotes the first tone mapping function, INPUT denotes aluminance signal which is extracted from the data signal, and OUTPUT1denotes a first output luminance signal which is obtained by performingthe first tone mapping on the luminance signal.

In exemplary embodiments, the second tone mapping function may beexpressed by [Equation 2] below:OUTPUT2=(1+α)×GTM(INPUT),   [Equation 2]where GTM denotes the first tone mapping function, INPUT denotes theluminance signal which is extracted from the data signal, α denotes thelocal weighted value, and OUTPUT2 denotes a second output luminancesignal which is obtained by performing the second tone mapping on theluminance signal.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention, and together with the description serve to explain theinventive concepts.

FIG. 1 is a flowchart illustrating a method of performing animage-adaptive tone mapping according to exemplary embodiments.

FIG. 2 is a diagram for describing the method of FIG. 1.

FIG. 3A is a graph illustrating an example of a first tone mappingfunction which is calculated by the method of FIG. 1.

FIG. 3B is a graph illustrating another example of a first tone mappingfunction which is calculated by the method of FIG. 1.

FIG. 4 is a graph illustrating a local weighted value which iscalculated by the method of FIG. 1.

FIG. 5 is a flowchart illustrating a method of performing animage-adaptive tone mapping according to exemplary embodiments.

FIG. 6 is a diagram for describing the method of FIG. 5.

FIG. 7 is a graph illustrating a local weighted value which iscalculated by the method of FIG. 5.

FIG. 8 is a block diagram illustrating a display device according to anexemplary embodiment.

FIG. 9 is a block diagram illustrating an electronic device according toan exemplary embodiment.

FIG. 10A is a perspective view illustrating an example in which theelectronic device of FIG. 9 is implemented as a smart phone.

FIG. 10B is a perspective view illustrating an example in which theelectronic device of FIG. 9 is implemented as a head mounted display(HMD) device.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of various exemplary embodiments of the invention. As usedherein “embodiments” are non-limiting examples of devices or methodsemploying one or more of the inventive concepts disclosed herein. It isapparent, however, that various exemplary embodiments may be practicedwithout these specific details or with one or more equivalentarrangements. In other instances, well-known structures and devices areshown in block diagram form in order to avoid unnecessarily obscuringvarious exemplary embodiments. Further, various exemplary embodimentsmay be different, but do not have to be exclusive. For example, specificshapes, configurations, and characteristics of an exemplary embodimentmay be used or implemented in another exemplary embodiment withoutdeparting from the inventive concepts.

Unless otherwise specified, the illustrated exemplary embodiments are tobe understood as providing exemplary features of varying detail of someways in which the inventive concepts may be implemented in practice.Therefore, unless otherwise specified, the features, components,modules, layers, films, panels, regions, and/or aspects, etc.(hereinafter individually or collectively referred to as “elements”), ofthe various embodiments may be otherwise combined, separated,interchanged, and/or rearranged without departing from the inventiveconcepts.

In the accompanying drawings, the size and relative sizes of elementsmay be exaggerated for clarity and/or descriptive purposes. When anexemplary embodiment may be implemented differently, a specific processorder may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order. Also, like reference numerals denote like elements.

When an element, such as a layer, is referred to as being “on,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, connected to, or coupled to the other element or layer orintervening elements or layers may be present. When, however, an elementor layer is referred to as being “directly on,” “directly connected to,”or “directly coupled to” another element or layer, there are nointervening elements or layers present. To this end, the term“connected” may refer to physical, electrical, and/or fluid connection,with or without intervening elements. Further, the D1-axis, the D2-axis,and the D3-axis are not limited to three axes of a rectangularcoordinate system, such as the x, y, and z-axes, and may be interpretedin a broader sense. For example, the D1-axis, the D2-axis, and theD3-axis may be perpendicular to one another, or may represent differentdirections that are not perpendicular to one another. For the purposesof this disclosure, “at least one of X, Y, and Z” and “at least oneselected from the group consisting of X, Y, and Z” may be construed as Xonly, Y only, Z only, or any combination of two or more of X, Y, and Z,such as, for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Although the terms “first,” “second,” etc. may be used herein todescribe various types of elements, these elements should not be limitedby these terms. These terms are used to distinguish one element fromanother element. Thus, a first element discussed below could be termed asecond element without departing from the teachings of the disclosure.

Spatially relative terms, such as “beneath,” “below,” “under,” “lower,”“above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), andthe like, may be used herein for descriptive purposes, and, thereby, todescribe one elements relationship to another element(s) as illustratedin the drawings. Spatially relative terms are intended to encompassdifferent orientations of an apparatus in use, operation, and/ormanufacture in addition to the orientation depicted in the drawings. Forexample, if the apparatus in the drawings is turned over, elementsdescribed as “below” or “beneath” other elements or features would thenbe oriented “above” the other elements or features. Thus, the exemplaryterm “below” can encompass both an orientation of above and below.Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90degrees or at other orientations), and, as such, the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises,” “comprising,” “includes,” and/or “including,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, components, and/orgroups thereof, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components,and/or groups thereof. It is also noted that, as used herein, the terms“substantially,” “about,” and other similar terms, are used as terms ofapproximation and not as terms of degree, and, as such, are utilized toaccount for inherent deviations in measured, calculated, and/or providedvalues that would be recognized by one of ordinary skill in the art.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure is a part. Terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and should not be interpreted in anidealized or overly formal sense, unless expressly so defined herein.

FIG. 1 is a flowchart illustrating a method of performing animage-adaptive tone mapping according to exemplary embodiments. FIG. 2is a diagram for describing the method of FIG. 1. FIG. 3A is a graphillustrating an example of a first tone mapping function which iscalculated by the method of FIG. 1. FIG. 3B is a graph illustratinganother example of a first tone mapping function which is calculated bythe method of FIG. 1. FIG. 4 is a graph illustrating a local weightedvalue which is calculated by the method of FIG. 1.

Referring to FIGS. 1 to 4, the method of FIG. 1 calculates anentire-grayscale luminance average, a low-grayscale luminance averageLGA, and a high-grayscale luminance average of an image frame to bedisplayed on a display panel 10 by analyzing a data signal correspondingto the image frame (S110); determines a first tone mapping function GTMto be applied to the image frame based on the entire-grayscale luminanceaverage, the low-grayscale luminance average LGA, and the high-grayscaleluminance average of the image frame (S120); divides (or classifies) thedisplay panel 10 into a plurality of display blocks 15 by grouping aplurality of pixels 11 included in the display panel 10 by location(S130); classifies the display blocks 15 into non-target display blocks,of which block luminance BIG (i.e., luminance which each display block15 is to implement in the image frame) is greater than the low-grayscaleluminance average LGA of the image frame, and target display blocks, ofwhich the block luminance BIG is less than the low-grayscale luminanceaverage LGA of the image frame (S140); performs a first tone mapping onthe image frame by applying the first tone mapping function GTM to eachof the non-target display blocks (S150); and performs a second tonemapping on the image frame by applying a second tone mapping function(1+α)×GTM to each of the target display blocks (S160), where the secondtone mapping function (1+α)×GTM is obtained by applying a local weightedvalue α to the first tone mapping function GTM. The method of FIG. 1 mayperform the steps S110, S120, S130, S140, S150, and S160 for respectiveimage frames to be displayed on the display panel 10.

Specifically, the method of FIG. 1 may calculate the entire-grayscaleluminance average, the low-grayscale luminance average LGA, and thehigh-grayscale luminance average of the image frame by analyzing thedata signal corresponding to the image frame to be displayed on thedisplay panel 10 (S110). In an exemplary embodiment, the data signalcorresponding to the image frame to be displayed on the display panel 10may be an RGB signal. In this case, the method of FIG. 1 may calculatethe entire-grayscale luminance average, the low-grayscale luminanceaverage LGA, and the high-grayscale luminance average of the image framebased on a luminance signal, which is extracted from the data signal.Specifically, the method of FIG. 1 may convert the data signal (i.e.,the RGB signal) corresponding to the image frame to be displayed on thedisplay panel 10 into an YCbCr signal and may calculate theentire-grayscale luminance average, the low-grayscale luminance averageLGA, and the high-grayscale luminance average of the image frame basedon the luminance signal (i.e., a Y signal) of the YCbCr signal. In anexemplary embodiment, the method of FIG. 1 may calculate theentire-grayscale luminance average of the image frame as an average ofpixel luminance (i.e., luminance which each pixel 11 is to implement inthe image frame) of all pixels 11 included in the display panel 10.Here, the method of FIG. 1 may classify the pixels 11 included in thedisplay panel 10 into high-grayscale luminance pixels, of which thepixel luminance is greater than the entire-grayscale luminance averageof the image frame and low-grayscale luminance pixels, of which thepixel luminance is less than the entire-grayscale luminance average ofthe image frame. In an exemplary embodiment, the method of FIG. 1 maydetermine the pixels 11, of which the pixel luminance is equal to theentire-grayscale luminance average of the image frame as thehigh-grayscale luminance pixels or the low-grayscale luminance pixelsaccording to given requirements. In an exemplary embodiment, the methodof FIG. 1 may calculate the low-grayscale luminance average LGA of theimage frame as an average of the pixel luminance of the low-grayscaleluminance pixels among the pixels 11 included in the display panel 10and may calculate the high-grayscale luminance average of the imageframe as an average of the pixel luminance of the high-grayscaleluminance pixels among the pixels 11 included in the display panel 10.

Subsequently, the method of FIG. 1 may determine the first tone mappingfunction GTM to be applied to the image frame based on theentire-grayscale luminance average, the low-grayscale luminance averageLGA, and the high-grayscale luminance average of the image frame (S120).For example, as illustrated in FIGS. 3A and 3B, the method of FIG. 1 mayderive the first tone mapping curve GTM using (or with respect to) areference function RM. Here, the reference function denotes a functionwhen the tone mapping is not performed. As described above, the methodof FIG. 1 may calculate the entire-grayscale luminance average, thelow-grayscale luminance average LGA, and the high-grayscale luminanceaverage of the image frame based on the luminance signal (i.e., the Ysignal) which is extracted from the data signal (i.e., the RGB signal)corresponding to the image frame to be displayed on the display panel10. Specifically, the method of FIG. 1 may convert the data signal(i.e., the RGB signal) corresponding to the image frame to be displayedon the display panel 10 into the YCbCr signal and may calculate theentire-grayscale luminance average, the low-grayscale luminance averageLGA, and the high-grayscale luminance average of the image frame basedon the luminance signal (i.e., the Y signal) of the YCbCr signal. Inthis case, the method of FIG. 1 may determine the first tone mappingfunction GTM to be applied to the image frame based on theentire-grayscale luminance average, the low-grayscale luminance averageLGA, and the high-grayscale luminance average of the image frame. Forexample, as illustrated in FIG. 3A, when a median value betweenpredetermined maximum luminance and the entire-grayscale luminanceaverage of the image frame is greater than the high-grayscale luminanceaverage of the image frame, the method of FIG. 1 may derive the firsttone mapping curve GTM by moving the first tone mapping curve GTMupwardly over the reference function RM in a high-grayscale section(i.e., indicated by INC1). In addition, when a median value betweenpredetermined minimum luminance and the entire-grayscale luminanceaverage of the image frame is less than the low-grayscale luminanceaverage LGA of the image frame, the method of FIG. 1 may derive thefirst tone mapping curve GTM by moving the first tone mapping curve GTMdownwardly under the reference function RM in a low-grayscale section(i.e., indicated by DEC1). For example, as illustrated in FIG. 3B, whenthe median value between the predetermined maximum luminance and theentire-grayscale luminance average of the image frame is greater thanthe high-grayscale luminance average of the image frame and when themedian value between the predetermined minimum luminance and theentire-grayscale luminance average of the image frame is greater thanthe low-grayscale luminance average LGA of the image frame, the methodof FIG. 1 may derive the first tone mapping curve GTM by moving thefirst tone mapping curve GTM upwardly over the reference function RM inan entire-grayscale section (i.e., indicated by INC2). However, derivingthe first tone mapping curve GTM is not limited thereto.

The method of FIG. 1 may divide the display panel 10 into the displayblocks 15 by grouping the pixels 11 included in the display panel 10 bylocation (S130). Thus, as illustrated in FIG. 2, the display panel 10may include one or more display blocks 15, and each of the displayblocks 15 may include one or more pixels 11. For convenience ofdescription, although it is described above that the step S130 isperformed after the steps S110 and S120, it should be understood thatthe step S130 can be performed prior to the steps S110 and S120. In anexemplary embodiment, a size and a shape of the display block 15 formedby grouping the pixels 11 of the display panel 10 by location may befixed. In this case, the method of FIG. 1 may divide the display panel10 into the display blocks 15 in the same size and in the same shape forrespective image frames. In another exemplary embodiment, the sizeand/or the shape of the display block 15 formed by grouping the pixels11 of the display panel 10 by location may be changed. In this case, themethod of FIG. 1 may divide the display panel 10 into the display blocks15 in a different size and/or in a different shape for respective imageframes or according to given requirements. When the display panel 10 isdivided into the display blocks 15, the method of FIG. 1 may calculatethe block luminance BIG of each display block 15. In an exemplaryembodiment, the method of FIG. 1 may calculate the block luminance BIGof each display block 15 as an average of the pixel luminance of thepixels 11 included in each display block 15. In another exemplaryembodiment, the method of FIG. 1 may calculate the block luminance BIGof each display block 15 as a weighted average of the pixel luminance ofthe pixels 11 included in each display block 15. In still anotherexemplary embodiment, the method of FIG. 1 may determine the blockluminance BIG of each display block 15 as a minimum grayscale amonggrayscales corresponding to the pixel luminance of the pixels 11included in each display block 15.

Next, the method of FIG. 1 may classify the display blocks 15 into thenon-target display blocks, of which the block luminance BIG is greaterthan the low-grayscale luminance average LGA of the image frame and thetarget display blocks, of which the block luminance BIG is less than thelow-grayscale luminance average LGA of the image frame (S140). In otherwords, the display blocks 15, of which the block luminance BIG isgreater than the low-grayscale luminance average LGA of the image framemay be determined as the non-target display blocks, and the displayblocks 15, of which the block luminance BIG is less than thelow-grayscale luminance average LGA of the image frame may be determinedas the target display blocks. In an exemplary embodiment, the method ofFIG. 1 may determine the display blocks 15, of which the block luminanceBIG is equal to the low-grayscale luminance average LGA of the imageframe as the target display blocks or the non-target display blocksaccording to given requirements. Subsequently, the method of FIG. 1 mayperform the first tone mapping on the image frame by applying the firsttone mapping function GTM to each of the non-target display blocks amongthe display blocks 15 (S150) and may perform the second tone mapping onthe image frame by applying the second tone mapping function (1+α)×GTMto each of the target display blocks among the display blocks 15 (S160),where the second tone mapping function (1+α)×GTM is obtained by applyingthe local weighted value α to the first tone mapping function GTM. In anexemplary embodiment, the first tone mapping function GTM may beexpressed by [Equation 1] below, and the second tone mapping function(1+α)×GTM may be expressed by [Equation 2] below:OUTPUT1=GTM(INPUT),   [Equation 1]where GTM denotes the first tone mapping function, INPUT denotes theluminance signal which is extracted from the data signal, and OUTPUT1denotes a first output luminance signal which is obtained by performingthe first tone mapping on the luminance signal.OUTPUT2=(1+α)×GTM(INPUT),   [Equation 2]where GTM denotes the first tone mapping function, INPUT denotes theluminance signal which is extracted from the data signal, a denotes thelocal weighted value, and OUTPUT2 denotes a second output luminancesignal which is obtained by performing the second tone mapping on theluminance signal.

As described above, for the pixels 11 included in the non-target displayblocks among the display blocks 15, the method of FIG. 1 may performonly a so-called global tone mapping. On the other hand, for the pixels11 included in the target display blocks among the display blocks 15,the method of FIG. 1 may perform the global tone mapping and as well asa so-called local tone mapping to complement the global tone mapping.Specifically, as illustrated in FIGS. 3A and 3B, for each of thenon-target display blocks among the display blocks 15, the method ofFIG. 1 may perform the first tone mapping on the image frame byoutputting the first output luminance signal OUTPUT1 which is obtainedby performing the first tone mapping on the luminance signal INPUT,which is extracted from the data signal, using the first tone mappingfunction GTM. In an exemplary embodiment, the method of FIG. 1 mayconvert the data signal (i.e., the RGB signal) into the YCbCr signal andmay calculate the entire-grayscale luminance average, the low-grayscaleluminance average LGA, and the high-grayscale luminance average of theimage frame based on the luminance signal INPUT (i.e., the Y signal) ofthe YCbCr signal. In this case, for each of the non-target displayblocks among the display blocks 15, the method of FIG. 1 may generatethe first output luminance signal OUTPUT1 (i.e., the Y′ signal) based onthe luminance signal INPUT (i.e., the Y signal) using the first tonemapping function GTM. Thus, the YCbCr signal may be converted into theY′Cb′Cr′ signal. Subsequently, for each of the non-target display blocksamong the display blocks 15, the method of FIG. 1 may convert theY′Cb′Cr′ signal into the R′G′B′ signal and then may display the imageframe based on the R′G′B′ signal. In this way, the method of FIG. 1 mayperform the first tone mapping on the image frame for each of thenon-target display blocks among the display blocks 15.

On the other hand, for each of the target display blocks among thedisplay blocks 15, the method of FIG. 1 may perform the second tonemapping on the image frame by outputting the second output luminancesignal OUTPUT2 which is obtained by performing the second tone mappingon the luminance signal INPUT, which is extracted from the data signal,using the second tone mapping function (1+α)×GTM. In an exemplaryembodiment, the method of FIG. 1 may convert the data signal (i.e., theRGB signal) into the YCbCr signal and may calculate the entire-grayscaleluminance average, the low-grayscale luminance average LGA, and thehigh-grayscale luminance average of the image frame based on theluminance signal INPUT (i.e., the Y signal) of the YCbCr signal. In thiscase, for each of the target display blocks among the display blocks 15,the method of FIG. 1 may generate the second output luminance signalOUTPUT2 (i.e., the Y′ signal) based on the luminance signal INPUT (i.e.,the Y signal) using the second tone mapping function (1+α)×GTM. Thus,the YCbCr signal may be converted into the Y′Cb′Cr′ signal.Subsequently, for each of the target display blocks among the displayblocks 15, the method of FIG. 1 may convert the Y′Cb′Cr′ signal into theR′G′B′ signal and then may display the image frame based on the R′G′B′signal. In this way, the method of FIG. 1 may perform the second tonemapping on the image frame for each of the target display blocks amongthe display blocks 15. Here, as illustrated in FIG. 4, the localweighted value α, which is applied to the first tone mapping functionGTM to generate the second tone mapping function (1+α)×GTM, may decreasewithin a predetermined weighted value range WR as a luminance ratiowhich is calculated by dividing the block luminance BIG of each targetdisplay block by the low-grayscale luminance average LGA of the imageframe increases. On the other hand, the local weighted value α, which isapplied to the first tone mapping function GTM to generate the secondtone mapping function (1+α)×GTM, may increase within the predeterminedweighted value range WR as the luminance ratio which is calculated bydividing the block luminance BIG of each target display block by thelow-grayscale luminance average LGA of the image frame decreases. Asdescribed above, for each of the target display blocks among the displayblocks 15, the method of FIG. 1 may further perform the simple localtone mapping to complement the global tone mapping by performing thesecond tone mapping on the image frame using the second tone mappingfunction (1+α)×GTM, which is obtained by applying the local weightedvalue α to the first tone mapping function GTM. Therefore, as comparedto a conventional image-adaptive tone mapping method, the method of FIG.1 may be easily implemented by hardware and may be performed inreal-time because an amount of computation is relatively small.

In brief, the method of FIG. 1 calculates the entire-grayscale luminanceaverage, the low-grayscale luminance average LGA, and the high-grayscaleluminance average of the image frame by analyzing the data signalcorresponding to the image frame to be displayed on the display panel10, determines the first tone mapping function GTM to be applied to theimage frame based on the entire-grayscale luminance average, thelow-grayscale luminance average LGA, and the high-grayscale luminanceaverage of the image frame, divides the display panel 10 into thedisplay blocks 15 by grouping the pixels 11 included in the displaypanel 10 by location, classifies the display blocks 15 into thenon-target display blocks and the target display blocks based on theblock luminance BIG of respective display blocks 15, performs the firsttone mapping on the image frame by applying the first tone mappingfunction GTM to each of the non-target display blocks among the displayblocks 15, and performs the second tone mapping on the image frame byapplying the second tone mapping function (1+α)×GTM to each of thetarget display blocks among the display blocks 15, where the second tonemapping function (1+α)×GTM is obtained by applying the local weightedvalue α to the first tone mapping function GTM. Thus, the method of FIG.1 may improve a contrast ratio of the image frame, may enhanceexpressive power of the low-grayscale region of the image frame (i.e.,may properly reflect characteristics of the low-grayscale region of theimage frame), and thus, may provide a high-quality image to a user. Asdescribed above, the method of FIG. 1 may improve a result (i.e., mayoutput the second output luminance signal OUPUT2 instead of the firstoutput luminance signal OUTPUT1 in response to the luminance signalINPUT) by applying the local weighted value α to the first tone mappingfunction GTM (i.e., the global tone mapping function) when the blockluminance BIG of the display block 15 is less than the low-grayscaleluminance average LGA of the image frame (i.e., the luminance of thelow-grayscale region of the image frame). In other words, the method ofFIG. 1 may reflect the block luminance BIG of the display block 15(i.e., average luminance information of the display block 15) to performthe image-adaptive tone mapping. As a result, the method of FIG. 1 mayenhance the expressive power of the low-grayscale region of the imageframe, as well as improve the contrast ratio of the image frame.

FIG. 5 is a flowchart illustrating a method of performing animage-adaptive tone mapping according to exemplary embodiments. FIG. 6is a diagram for describing the method of FIG. 5. FIG. 7 is a graphillustrating a local weighted value, which is calculated by the methodof FIG. 5.

Referring to FIGS. 5 to 7, the method of FIG. 5 calculates anentire-grayscale luminance average, a low-grayscale luminance average,and a high-grayscale luminance average of an image frame to be displayedon a display panel 10 by analyzing a data signal corresponding to theimage frame (S210); determines a first tone mapping function GTM to beapplied to the image frame based on the entire-grayscale luminanceaverage, the low-grayscale luminance average, and the high-grayscaleluminance average of the image frame (S220); divides the display panel10 into a plurality of display blocks 15 by grouping a plurality ofpixels 11 included in the display panel 10 by location (S230);classifies the display blocks 15 into non-target display blocks, ofwhich block luminance BIG (i.e., luminance which each display block 15is to implement in the image frame) is greater than a block luminanceaverage AGA of N adjacent display blocks ADB, and target display blocks,of which the block luminance BIG is less than the block luminanceaverage AGA of the N adjacent display blocks ADB (S240); performs afirst tone mapping on the image frame by applying the first tone mappingfunction GTM to each of the non-target display blocks (S250); andperforms a second tone mapping on the image frame by applying a secondtone mapping function (1+α)×GTM to each of the target display blocks(S260), where the second tone mapping function (1+α)×GTM is obtained byapplying a local weighted value α to the first tone mapping functionGTM. The method of FIG. 5 may perform the steps S210, S220, S230, S240,S250, and S260 for respective image frames to be displayed on thedisplay panel 10.

Specifically, the method of FIG. 5 may calculate the entire-grayscaleluminance average, the low-grayscale luminance average, and thehigh-grayscale luminance average of the image frame by analyzing thedata signal corresponding to the image frame to be displayed on thedisplay panel 10 (S210). In an exemplary embodiment, the data signalcorresponding to the image frame to be displayed on the display panel 10may be an RGB signal. In this case, the method of FIG. 5 may calculatethe entire-grayscale luminance average, the low-grayscale luminanceaverage, and the high-grayscale luminance average of the image framebased on a luminance signal, which is extracted from the data signal.Specifically, the method of FIG. 5 may convert the data signal (i.e.,the RGB signal) corresponding to the image frame to be displayed on thedisplay panel 10 into an YCbCr signal and may calculate theentire-grayscale luminance average, the low-grayscale luminance average,and the high-grayscale luminance average of the image frame based on theluminance signal (i.e., a Y signal) of the YCbCr signal. In an exemplaryembodiment, the method of FIG. 5 may calculate the entire-grayscaleluminance average of the image frame as an average of pixel luminance(i.e., luminance which each pixel 11 is to implement in the image frame)of all pixels 11 included in the display panel 10. Here, the method ofFIG. 5 may classify the pixels 11 included in the display panel 10 intohigh-grayscale luminance pixels, of which the pixel luminance is greaterthan the entire-grayscale luminance average of the image frame andlow-grayscale luminance pixels, of which the pixel luminance is lessthan the entire-grayscale luminance average of the image frame. In anexemplary embodiment, the method of FIG. 5 may determine the pixels 11,of which the pixel luminance is equal to the entire-grayscale luminanceaverage of the image frame as the high-grayscale luminance pixels or thelow-grayscale luminance pixels according to given requirements. In anexemplary embodiment, the method of FIG. 5 may calculate thelow-grayscale luminance average of the image frame as an average of thepixel luminance of the low-grayscale luminance pixels among the pixels11 included in the display panel 10 and may calculate the high-grayscaleluminance average of the image frame as an average of the pixelluminance of the high-grayscale luminance pixels among the pixels 11included in the display panel 10.

Subsequently, the method of FIG. 5 may determine the first tone mappingfunction GTM to be applied to the image frame based on theentire-grayscale luminance average, the low-grayscale luminance average,and the high-grayscale luminance average of the image frame (S220). Asdescribed above, the method of FIG. 5 may calculate the entire-grayscaleluminance average, the low-grayscale luminance average, and thehigh-grayscale luminance average of the image frame based on theluminance signal (i.e., the Y signal) which is extracted from the datasignal (i.e., the RGB signal) corresponding to the image frame to bedisplayed on the display panel 10. Specifically, the method of FIG. 5may convert the data signal (i.e., the RGB signal) corresponding to theimage frame to be displayed on the display panel 10 into the YCbCrsignal and may calculate the entire-grayscale luminance average, thelow-grayscale luminance average, and the high-grayscale luminanceaverage of the image frame based on the luminance signal (i.e., the Ysignal) of the YCbCr signal. In this case, the method of FIG. 5 maydetermine the first tone mapping function GTM to be applied to the imageframe based on the entire-grayscale luminance average, the low-grayscaleluminance average, and the high-grayscale luminance average of the imageframe. Since these are described above with reference to FIGS. 3A and3B, duplicate descriptions related thereto will not be repeated.

The method of FIG. 5 may divide the display panel 10 into the displayblocks 15 by grouping the pixels 11 included in the display panel 10 bylocation (S230). Thus, as illustrated in FIG. 6, the display panel 10may include one or more display blocks 15, and each of the displayblocks 15 may include one or more pixels 11. For convenience ofdescription, although it is described above that the step S230 isperformed after the steps S210 and S220, it should be understood thatthe step S230 can be performed prior to the steps S210 and S220. In anexemplary embodiment, a size and a shape of the display block 15 formedby grouping the pixels 11 of the display panel 10 by location may befixed. In this case, the method of FIG. 5 may divide the display panel10 into the display blocks 15 in the same size and in the same shape forrespective image frames. In another exemplary embodiment, the sizeand/or the shape of the display block 15 formed by grouping the pixels11 of the display panel 10 by location may be changed. In this case, themethod of FIG. 5 may divide the display panel 10 into the display blocks15 in a different size and/or in a different shape for respective imageframes or according to given requirements. When the display panel 10 isdivided into the display blocks 15, the method of FIG. 5 may calculatethe block luminance BIG of each display block 15. In an exemplaryembodiment, the method of FIG. 5 may calculate the block luminance BIGof each display block 15 as an average of the pixel luminance of thepixels 11 included in each display block 15. In another exemplaryembodiment, the method of FIG. 5 may calculate the block luminance BIGof each display block 15 as a weighted average of the pixel luminance ofthe pixels 11 included in each display block 15. In still anotherexemplary embodiment, the method of FIG. 5 may determine the blockluminance BIG of each display block 15 as a minimum grayscale amonggrayscales corresponding to the pixel luminance of the pixels 11included in each display block 15.

Next, the method of FIG. 5 may classify the display blocks 15 into thenon-target display blocks, of which the block luminance BIG is greaterthan the block luminance average AGA of the N adjacent display blocksADB, and the target display blocks, of which the block luminance BIG isless than the block luminance average AGA of the N adjacent displayblocks ADB (S240). In other words, the display blocks 15, of which theblock luminance BIG is greater than the block luminance average AGA ofthe N adjacent display blocks ADB may be determined as the non-targetdisplay blocks, and the display blocks 15, of which the block luminanceBIG is less than the block luminance average AGA of the N adjacentdisplay blocks ADB may be determined as the target display blocks. Inexemplary embodiments, the method of FIG. 5 may determine the displayblocks 15, of which the block luminance BIG is equal to the blockluminance average AGA of the N adjacent display blocks ADB as the targetdisplay blocks or the non-target display blocks according to givenrequirements. In an exemplary embodiment, as illustrated in FIG. 6, whenthe block luminance average AGA of the N adjacent display blocks ADB iscalculated, the N adjacent display blocks ADB may not include a displayblock DB to be classified. In this case, the block luminance BIG of thedisplay block DB to be classified may be compared with the blockluminance average AGA of the N adjacent display blocks ADB surroundingthe display block DB to be classified. For example, as illustrated inFIG. 6, the display block DB to be classified may be surrounded by eightadjacent display blocks ADB, and the block luminance BIG of the displayblock DB to be classified may be compared with the block luminanceaverage AGA of the eight adjacent display blocks ADB. In anotherexemplary embodiment, when the block luminance average AGA of the Nadjacent display blocks ADB is calculated, the N adjacent display blocksADB may include a display block DB to be classified. In this case, theblock luminance BIG of the display block DB to be classified may becompared with the block luminance average AGA of the N adjacent displayblocks ADB including the display block DB to be classified. For example,the block luminance average AGA of nine adjacent display blocks ADB(i.e., 3×3 display blocks 15) including the display block DB to beclassified may be calculated, and the block luminance BIG of the displayblock DB to be classified may be compared with the block luminanceaverage AGA of the nine adjacent display blocks ADB including thedisplay block DB to be classified.

Subsequently, the method of FIG. 5 may perform the first tone mapping onthe image frame by applying the first tone mapping function GTM to eachof the non-target display blocks among the display blocks 15 (S250) andmay perform the second tone mapping on the image frame by applying thesecond tone mapping function (1+α)×GTM to each of the target displayblocks among the display blocks 15 (S260), where the second tone mappingfunction (1+α)×GTM is obtained by applying the local weighted value α tothe first tone mapping function GTM. In an exemplary embodiment, thefirst tone mapping function GTM may be expressed by [Equation 1] above,and the second tone mapping function (1+α)×GTM may be expressed by[Equation 2] above. As described above, for the pixels 11 included inthe non-target display blocks among the display blocks 15, the method ofFIG. 5 may perform only a so-called global tone mapping. On the otherhand, for the pixels 11 included in the target display blocks among thedisplay blocks 15, the method of FIG. 5 may perform the global tonemapping and may further perform a so-called local tone mapping tocomplement the global tone mapping. Specifically, for each of thenon-target display blocks among the display blocks 15, the method ofFIG. 5 may perform the first tone mapping on the image frame byoutputting the first output luminance signal which is obtained byperforming the first tone mapping on the luminance signal, which isextracted from the data signal, using the first tone mapping functionGTM. In an exemplary embodiment, the method of FIG. 5 may convert thedata signal (i.e., the RGB signal) into the YCbCr signal and maycalculate the entire-grayscale luminance average, the low-grayscaleluminance average, and the high-grayscale luminance average of the imageframe based on the luminance signal (i.e., the Y signal) of the YCbCrsignal. In this case, for each of the non-target display blocks amongthe display blocks 15, the method of FIG. 5 may generate the firstoutput luminance signal (i.e., the Y′ signal) based on the luminancesignal (i.e., the Y signal) using the first tone mapping function GTM.Thus, the YCbCr signal may be converted into the Y′Cb′Cr′ signal.Subsequently, for each of the non-target display blocks among thedisplay blocks 15, the method of FIG. 5 may convert the Y′Cb′Cr′ signalinto the R′G′B′ signal and then may display the image frame based on theR′G′B′ signal. In this way, the method of FIG. 5 may perform the firsttone mapping on the image frame for each of the non-target displayblocks among the display blocks 15.

On the other hand, for each of the target display blocks among thedisplay blocks 15, the method of FIG. 5 may perform the second tonemapping on the image frame by outputting the second output luminancesignal which is obtained by performing the second tone mapping on theluminance signal, which is extracted from the data signal, using thesecond tone mapping function (1+α)×GTM. In an exemplary embodiment, themethod of FIG. 5 may convert the data signal (i.e., the RGB signal) intothe YCbCr signal and may calculate the entire-grayscale luminanceaverage, the low-grayscale luminance average, and the high-grayscaleluminance average of the image frame based on the luminance signal(i.e., the Y signal) of the YCbCr signal. In this case, for each of thetarget display blocks among the display blocks 15, the method of FIG. 5may generate the second output luminance signal (i.e., the Y′ signal)based on the luminance signal (i.e., the Y signal) using the second tonemapping function (1+α)×GTM. Thus, the YCbCr signal may be converted intothe Y′Cb′Cr′ signal. Subsequently, for each of the target display blocksamong the display blocks 15, the method of FIG. 5 may convert theY′Cb′Cr′ signal into the R′G′B′ signal and then may display the imageframe based on the R′G′B′ signal. In this way, the method of FIG. 5 mayperform the second tone mapping on the image frame for each of thetarget display blocks among the display blocks 15. Here, as illustratedin FIG. 7, the local weighted value α which is applied to the first tonemapping function GTM to generate the second tone mapping function(1+α)×GTM may decrease within a predetermined weighted value range WR asa luminance ratio which is calculated by dividing the block luminanceBIG of each target display block by the block luminance average AGA ofthe N adjacent display blocks ADB increases. On the other hand, thelocal weighted value α which is applied to the first tone mappingfunction GTM to generate the second tone mapping function (1+α)×GTM mayincrease within the predetermined weighted value range WR as theluminance ratio which is calculated by dividing the block luminance BIGof each target display block by the block luminance average AGA of the Nadjacent display blocks ADB decreases. As described above, for each ofthe target display blocks among the display blocks 15, the method ofFIG. 5 may further perform the simple local tone mapping to complementthe global tone mapping by performing the second tone mapping on theimage frame using the second tone mapping function (1+α)×GTM which isobtained by applying the local weighted value α to the first tonemapping function GTM. Therefore, as compared to a conventionalimage-adaptive tone mapping method, the method of FIG. 5 may be easilyimplemented by hardware and may be performed in real-time because anamount of computation is relatively small.

In brief, the method of FIG. 5 may calculate the entire-grayscaleluminance average, the low-grayscale luminance average, and thehigh-grayscale luminance average of the image frame by analyzing thedata signal corresponding to the image frame to be displayed on thedisplay panel 10, may determine the first tone mapping function GTM tobe applied to the image frame based on the entire-grayscale luminanceaverage, the low-grayscale luminance average, and the high-grayscaleluminance average of the image frame, may divide the display panel 10into the display blocks 15 by grouping the pixels 11 included in thedisplay panel 10 by location, may classify the display blocks 15 intothe non-target display blocks and the target display blocks based on theblock luminance BIG of respective display blocks 15, may perform thefirst tone mapping on the image frame by applying the first tone mappingfunction GTM to each of the non-target display blocks among the displayblocks 15, and may perform the second tone mapping on the image frame byapplying the second tone mapping function (1+α)×GTM to each of thetarget display blocks among the display blocks 15, where the second tonemapping function (1+α)×GTM is obtained by applying the local weightedvalue α to the first tone mapping function GTM. Thus, the method of FIG.5 may improve a contrast ratio of the image frame, may enhanceexpressive power of the low-grayscale region of the image frame (i.e.,may properly reflect characteristics of the low-grayscale region of theimage frame), and thus, may provide a high-quality image to a user. Asdescribed above, the method of FIG. 5 may improve a result (i.e., mayoutput the second output luminance signal instead of the first outputluminance signal in response to the luminance signal) by applying thelocal weighted value α to the first tone mapping function GTM (i.e., theglobal tone mapping function) when the block luminance BIG of thedisplay block 15 is less than the block luminance average AGA of the Nadjacent display blocks ADB. In other words, the method of FIG. 5 mayreflect the block luminance BIG of the display block 15 (i.e., averageluminance information of the display block 15) to perform theimage-adaptive tone mapping. As a result, the method of FIG. 5 mayenhance the expressive power of the low-grayscale region of the imageframe as well as improve the contrast ratio of the image frame.

FIG. 8 is a block diagram illustrating a display device according to anexemplary embodiment.

Referring to FIG. 8, the display device 100 may include a display panel110 and a display panel driving circuit 120. In an exemplary embodiment,the display device 100 may be an organic light emitting display (OLED)device. In another exemplary embodiment, the display device 100 may be aliquid crystal display (LCD) device. However, the display device 100 ofthe inventive concepts is not limited thereto.

The display panel 110 may include a plurality of pixels 111. Here, thepixels 111 may be arranged in various forms (e.g., a matrix form, etc)in the display panel 110. The display panel driving circuit 120 maydrive the display panel 110. In an exemplary embodiment, the displaypanel driving circuit 120 may include a scan driver, a data driver, anda timing controller. The display panel 110 may be connected to the scandriver via scan lines. The display panel 110 may be connected to thedata driver via data lines. The scan driver may provide a scan signal SSto the pixels 111 included in the display panel 110 via the scan lines.The data driver may provide a tone-mapped data signal DS′ to the pixels111 included in the display panel 110 via the data lines. The timingcontroller may generate and provide a plurality of control signals tothe scan driver, the data driver, etc to control the scan driver, thedata driver, etc. In an exemplary embodiment, the timing controller mayperform a given processing (e.g., a deterioration compensationprocessing, etc) on a data signal DS input from an external component.In an exemplary embodiment, when the display device 100 is the OLEDdevice, the display panel driving circuit 120 may further include anemission control driver. In this case, the emission control driver maybe connected to the display panel 110 via emission control-lines. Theemission control driver may provide an emission control signal to thepixels 111 included in the display panel 110 via the emissioncontrol-lines. In an exemplary embodiment, when the display device 100is the LCD device, the display device 100 may further include abacklight unit that radiates light to the display panel 110.

The display panel driving circuit 120 may enhance an image quality byimproving a contrast ratio of an image frame by performing a tonemapping on respective image frames to be displayed on the display panel110. For example, when the data signal DS corresponding to the imageframe to be displayed on the display panel 110 is an RGB signal, thedisplay panel driving circuit 120 may perform the tone mapping on theimage frame by converting the RGB signal into an YCbCr signal, byconverting the YCbCr signal into an Y′Cb′Cr′ signal based on a firsttone mapping function and a second tone mapping function, by convertingthe Y′Cb′Cr′ signal into an R′G′B′ signal, and by displaying the imageframe based on the R′G′B′ signal. To this end, the display panel drivingcircuit 120 may calculate an entire-grayscale luminance average, alow-grayscale luminance average, and a high-grayscale luminance averageof an image frame to be displayed on the display panel 110 by analyzingthe data signal DS corresponding to the image frame, may determine thefirst tone mapping function to be applied to the image frame based onthe entire-grayscale luminance average, the low-grayscale luminanceaverage, and the high-grayscale luminance average of the image frame,may divide the display panel 110 into display blocks by grouping thepixels 111 included in the display panel 110 by location, may classifythe display blocks into non-target display blocks and target displayblocks based on block luminance of respective display blocks, mayperform a first tone mapping on the image frame by applying the firsttone mapping function to each of the non-target display blocks, and mayperform a second tone mapping on the image frame by applying the secondtone mapping function to each of the target display blocks, where thesecond tone mapping function is obtained by applying a local weightedvalue to the first tone mapping function. Here, the first tone mappingfunction may be expressed by [Equation 1] above, and the second tonemapping function may be expressed by [Equation 2] above.

In an exemplary embodiment, the display panel driving circuit 120 mayclassify the display blocks into the non-target display blocks, of whichthe block luminance is greater than the low-grayscale luminance averageof the image frame and the target display blocks, of which the blockluminance is less than the low-grayscale luminance average of the imageframe. Specifically, the display panel driving circuit 120 may calculatethe entire-grayscale luminance average, the low-grayscale luminanceaverage, and the high-grayscale luminance average of the image frame byanalyzing the data signal DS corresponding to the image frame to bedisplayed on the display panel 110, may determine the first tone mappingfunction to be applied to the image frame based on the entire-grayscaleluminance average, the low-grayscale luminance average, and thehigh-grayscale luminance average of the image frame, may divide thedisplay panel 110 into the display blocks by grouping the pixels 111included in the display panel 110 by location, may classify the displayblocks into the non-target display blocks, of which the block luminanceis greater than the low-grayscale luminance average and the targetdisplay blocks, of which the block luminance is less than thelow-grayscale luminance average, may perform the first tone mapping onthe image frame by applying the first tone mapping function to each ofthe non-target display blocks, and may perform the second tone mappingon the image frame by applying the second tone mapping function to eachof the target display blocks, where the second tone mapping function isobtained by applying the local weighted value to the first tone mappingfunction. As described above, for each of the non-target display blocksamong the display blocks, the display panel driving circuit 120 mayconvert the YCbCr signal into the Y′Cb′Cr′ signal by generating thefirst output luminance signal (i.e., Y′ signal) based on the luminancesignal (i.e., Y signal) using the first tone mapping function, mayconvert the Y′Cb′Cr′ signal into the R′G′B′ signal, and then may displaythe image frame based on the R′G′B′ signal. That is, for each of thenon-target display blocks among the display blocks, the display paneldriving circuit 120 may perform the first tone mapping on the imageframe. On the other hand, for each of the target display blocks amongthe display blocks, the display panel driving circuit 120 may convertthe YCbCr signal into the Y′Cb′Cr′ signal by generating the secondoutput luminance signal (i.e., Y′ signal) based on the luminance signal(i.e., Y signal) using the second tone mapping function, may convert theY′Cb′Cr′ signal into the R′G′B′ signal, and then may display the imageframe based on the R′G′B′ signal. That is, for each of the targetdisplay blocks among the display blocks, the display panel drivingcircuit 120 may perform the second tone mapping on the image frame.

In another exemplary embodiment, the display panel driving circuit 120may classify the display blocks into the non-target display blocks, ofwhich the block luminance is greater than a block luminance average of Nadjacent display blocks, and the target display blocks, of which theblock luminance is less than the block luminance average of the Nadjacent display blocks. Specifically, the display panel driving circuit120 may calculate the entire-grayscale luminance average, thelow-grayscale luminance average, and the high-grayscale luminanceaverage of the image frame by analyzing the data signal DS correspondingto the image frame to be displayed on the display panel 110, maydetermine the first tone mapping function to be applied to the imageframe based on the entire-grayscale luminance average, the low-grayscaleluminance average, and the high-grayscale luminance average of the imageframe, may divide the display panel 110 into the display blocks bygrouping the pixels 111 included in the display panel 110 by location,may classify the display blocks into the non-target display blocks, ofwhich the block luminance is greater than the block luminance average ofthe N adjacent display blocks and the target display blocks, of whichthe block luminance is less than the block luminance average of the Nadjacent display blocks, where the N adjacent display blocks may or maynot include a display block to be classified, may perform the first tonemapping on the image frame by applying the first tone mapping functionto each of the non-target display blocks, and may perform the secondtone mapping on the image frame by applying the second tone mappingfunction to each of the target display blocks, where the second tonemapping function is obtained by applying the local weighted value to thefirst tone mapping function. As described above, for each of thenon-target display blocks among the display blocks, the display paneldriving circuit 120 may convert the YCbCr signal into the Y′Cb′Cr′signal by generating the first output luminance signal (i.e., Y′ signal)based on the luminance signal (i.e., Y signal) using the first tonemapping function, may convert the Y′Cb′Cr′ signal into the R′G′B′signal, and then may display the image frame based on the R′G′B′ signal.That is, for each of the non-target display blocks among the displayblocks, the display panel driving circuit 120 may perform the first tonemapping on the image frame. On the other hand, for each of the targetdisplay blocks among the display blocks, the display panel drivingcircuit 120 may convert the YCbCr signal into the Y′Cb′Cr′ signal bygenerating the second output luminance signal (i.e., Y′ signal) based onthe luminance signal (i.e., Y signal) using the second tone mappingfunction, may convert the Y′Cb′Cr′ signal into the R′G′B′ signal, andthen may display the image frame based on the R′G′B′ signal. That is,for each of the target display blocks among the display blocks, thedisplay panel driving circuit 120 may perform the second tone mapping onthe image frame.

As described above, for the pixels 111 included in the non-targetdisplay blocks among the display blocks of the display panel 110, thedisplay panel driving circuit 120 may perform only a so-called globaltone mapping. On the other hand, for the pixels 111 included in thetarget display blocks among the display blocks of the display panel 110,the display panel driving circuit 120 may perform the global tonemapping and may further perform a so-called local tone mapping tocomplement the global tone mapping. In brief, the display device 100 mayperform the local tone mapping which complements the global tone mappingin a simple way by calculating the entire-grayscale luminance average,the low-grayscale luminance average, and the high-grayscale luminanceaverage of the image frame by analyzing the data signal DS correspondingto the image frame to be displayed on the display panel 110, bydetermining the first tone mapping function to be applied to the imageframe based on the entire-grayscale luminance average, the low-grayscaleluminance average, and the high-grayscale luminance average of the imageframe, by dividing the display panel 110 into display blocks by groupingthe pixels 111 included in the display panel 110 by location, byclassifying the display blocks into the non-target display blocks andthe target display blocks based on the block luminance of respectivedisplay blocks, by performing the first tone mapping on the image frameby applying the first tone mapping function to each of the non-targetdisplay blocks, and by performing the second tone mapping on the imageframe by applying the second tone mapping function to each of the targetdisplay blocks, where the second tone mapping function is obtained byapplying the local weighted value to the first tone mapping function.Thus, the display device 100 may perform an image-adaptive tone mappingin real-time while easily implementing the image-adaptive tone mapping.As a result, the display device 100 may improve a contrast ratio of theimage frame, may enhance expressive power of the low-grayscale region ofthe image frame (i.e., may properly reflect characteristics of thelow-grayscale region of the image frame), and thus may provide ahigh-quality image to a user. Although it is described above that thedisplay device 100 includes the display panel 110 and the display paneldriving circuit 120, in an exemplary embodiment, the display device 100may further include other components (e.g., a deterioration compensationcircuit for performing deterioration compensation on the pixels 111included in the display panel 110, etc).

FIG. 9 is a block diagram illustrating an electronic device according toexemplary embodiments. FIG. 10A is a perspective view illustrating anexample in which the electronic device of FIG. 9 is implemented as asmart phone. FIG. 10B is a perspective view illustrating an example inwhich the electronic device of FIG. 9 is implemented as a head mounteddisplay (HMD) device.

Referring to FIGS. 9 to 10B, the electronic device 500 may include aprocessor 510, a memory device 520, a storage device 530, aninput/output (I/O) device 540, a power supply 550, and a display device560. Here, the display device 560 may be the display device 100 of FIG.8. In addition, the electronic device 500 may further include aplurality of ports for communicating with a video card, a sound card, amemory card, a universal serial bus (USB) device, other electronicdevices, etc. In an exemplary embodiment, as illustrated in FIG. 10A,the electronic device 500 may be implemented as a smart phone. Inanother exemplary embodiment, as illustrated in FIG. 10B, the electronicdevice 500 may be implemented as an HMD device. However, the electronicdevice 500 is not limited thereto. For example, the electronic device500 may be implemented as a television, a cellular phone, a video phone,a smart pad, a smart watch, a tablet PC, a car navigation system, acomputer monitor, a laptop, etc.

The processor 510 may perform various computing functions. The processor510 may be a micro processor, a central processing unit (CPU), anapplication processor (AP), etc. The processor 510 may be coupled toother components via an address bus, a control bus, a data bus, etc.Further, the processor 510 may be coupled to an extended bus, such as aperipheral component interconnection (PCI) bus. The memory device 520may store data for operations of the electronic device 500. For example,the memory device 520 may include at least one non-volatile memorydevice such as an erasable programmable read-only memory (EPROM) device,an electrically erasable programmable read-only memory (EEPROM) device,a flash memory device, a phase change random access memory (PRAM)device, a resistance random access memory (RRAM) device, a nano floatinggate memory (NFGM) device, a polymer random access memory (PoRAM)device, a magnetic random access memory (MRAM) device, a ferroelectricrandom access memory (FRAM) device, etc, and/or at least one volatilememory device such as a dynamic random access memory (DRAM) device, astatic random access memory (SRAM) device, a mobile DRAM device, etc.The storage device 530 may include a solid state drive (SSD) device, ahard disk drive (HDD) device, a CD-ROM device, etc. The I/O device 540may include an input device such as a keyboard, a keypad, a mousedevice, a touchpad, a touch-screen, etc, and an output device such as aprinter, a speaker, etc. In an exemplary embodiment, the display device560 may be included in the I/O device 540. The power supply 550 mayprovide power for operations of the electronic device 500.

The display device 560 may be coupled to other components via buses orother communication links. In an exemplary embodiment, the displaydevice 560 may be an OLED device. In another exemplary embodiment, thedisplay device 560 may be an LCD device. However, the display device 560is not limited thereto. As described above, the display device 560 mayperform an image-adaptive tone mapping in real-time while easilyimplementing the image-adaptive tone mapping. Thus, the display device560 may improve a contrast ratio of an image frame, may enhanceexpressive power of a low-grayscale region of the image frame, and thusmay provide a high-quality image to a user. To this end, the displaydevice 560 includes a display panel and a display panel driving circuitfor driving the display panel. The display panel includes a plurality ofpixels. Specifically, the display panel driving circuit calculates anentire-grayscale luminance average, a low-grayscale luminance average,and a high-grayscale luminance average of an image frame to be displayedon the display panel by analyzing a data signal corresponding to theimage frame; determines a first tone mapping function to be applied tothe image frame based on the entire-grayscale luminance average, thelow-grayscale luminance average, and the high-grayscale luminanceaverage of the image frame; divides the display panel into displayblocks by grouping the pixels included in the display panel by location;classifies the display blocks into non-target display blocks and targetdisplay blocks based on block luminance of respective display blocks;performs a first tone mapping on the image frame by applying the firsttone mapping function to each of the non-target display blocks; andperforms a second tone mapping on the image frame by applying a secondtone mapping function to each of the target display blocks, where thesecond tone mapping function is obtained by applying a local weightedvalue to the first tone mapping function. Here, the first tone mappingfunction (i.e., a global tone mapping function) may be expressed by[Equation 1] above, and the second tone mapping function (i.e., a tonemapping function which is obtained by applying the local weighted valueto the global tone mapping function) may be expressed by [Equation 2]above. In an exemplary embodiment, the display panel driving circuit mayclassify the display blocks into the non-target display blocks, of whichthe block luminance is greater than the low-grayscale luminance averageof the image frame and the target display blocks, of which the blockluminance is less than the low-grayscale luminance average of the imageframe. In another exemplary embodiment, the display panel drivingcircuit may classify the display blocks into the non-target displayblocks, of which the block luminance is greater than a block luminanceaverage of N adjacent display blocks and the target display blocks, ofwhich the block luminance is less than the block luminance average ofthe N adjacent display blocks, where the N adjacent display blocks mayor may not include a display block to be classified. Since the displaydevice 560 is described above, duplicated description related theretowill not be repeated.

Therefore, a method of performing an image-adaptive tone mappingaccording to exemplary embodiments may perform a local tone mappingwhich complements a global tone mapping in a simple way by calculatingan entire-grayscale luminance average, a low-grayscale luminanceaverage, and a high-grayscale luminance average of an image frame to bedisplayed on a display panel by analyzing a data signal corresponding tothe image frame, by determining a first tone mapping function to beapplied to the image frame based on the entire-grayscale luminanceaverage, the low-grayscale luminance average, and the high-grayscaleluminance average of the image frame, by dividing the display panel intodisplay blocks by grouping pixels included in the display panel bylocation, by classifying the display blocks into non-target displayblocks and target display blocks based on block luminance of respectivedisplay blocks, by performing a first tone mapping on the image frame byapplying the first tone mapping function to each of the non-targetdisplay blocks, and by performing a second tone mapping on the imageframe by applying a second tone mapping function to each of the targetdisplay blocks, where the second tone mapping function is obtained byapplying a local weighted value to the first tone mapping function.Thus, the method of performing the image-adaptive tone mapping mayimprove a contrast ratio of the image frame, may enhance expressivepower of a low-grayscale region of the image frame (i.e., may properlyreflect characteristics of the low-grayscale region of the image frame),and thus may provide a high-quality image to a user (or viewer).

In addition, a display device employing the method of performing theimage-adaptive tone mapping according to exemplary embodiments mayperform an image-adaptive tone mapping in real-time while easilyimplementing the image-adaptive tone mapping. Thus, the display devicemay improve a contrast ratio of the image frame, may enhance expressivepower of the low-grayscale region of the image frame, and thus, mayprovide a high-quality image to a user.

The present inventive concept may be applied to a display device, and anelectronic device including the display device. For example, the presentinventive concept may be applied to a cellular phone, a smart phone, avideo phone, a smart pad, a smart watch, a tablet PC, a car navigationsystem, a television, a computer monitor, a laptop, a digital camera, anHMD device, etc.

Although certain exemplary embodiments have been described herein, otherembodiments and modifications will be apparent from this description.Accordingly, the inventive concepts are not limited to such embodiments,but rather to the broader scope of the appended claims and variousobvious modifications and equivalent arrangements as would be apparentto a person of ordinary skill in the art.

What is claimed is:
 1. A method of performing an image-adaptive tonemapping, the method comprising: calculating an entire-grayscaleluminance average, a low-grayscale luminance average, and ahigh-grayscale luminance average of an image frame to be displayed on adisplay panel by analyzing a data signal corresponding to the imageframe; determining a first tone mapping function to be applied to theimage frame based on the entire-grayscale luminance average, thelow-grayscale luminance average, and the high-grayscale luminanceaverage; dividing the display panel into a plurality of display blocksby grouping a plurality of pixels included in the display panel bylocation; classifying the display blocks into non-target display blocks,of which block luminance is greater than the low-grayscale luminanceaverage, and target display blocks, of which the block luminance is lessthan the low-grayscale luminance average; performing a first tonemapping on the image frame by applying the first tone mapping functionto each of the non-target display blocks; and performing a second tonemapping on the image frame by applying a second tone mapping function toeach of the target display blocks, the second tone mapping functionbeing obtained by applying a local weighted value to the first tonemapping function.
 2. The method of claim 1, wherein the first tonemapping function is expressed by [Equation 1] below:OUTPUT1=GTM(INPUT),   [Equation 1] where GTM denotes the first tonemapping function, INPUT denotes a luminance signal which is extractedfrom the data signal, and OUTPUT1 denotes a first output luminancesignal which is obtained by performing the first tone mapping on theluminance signal.
 3. The method of claim 2, wherein the second tonemapping function is expressed by [Equation 2] below:OUTPUT2=(1+α)×GTM(INPUT),   [Equation 2] where GTM denotes the firsttone mapping function, INPUT denotes the luminance signal which isextracted from the data signal, a denotes the local weighted value, andOUTPUT2 denotes a second output luminance signal which is obtained byperforming the second tone mapping on the luminance signal.
 4. Themethod of claim 3, wherein: the local weighted value decreases within apredetermined weighted value range as a luminance ratio, which iscalculated by dividing the block luminance of the each of the targetdisplay blocks by the low-grayscale luminance average, increases; andthe local weighted value increases within the predetermined weightedvalue range as the luminance ratio decreases.
 5. The method of claim 1,wherein: the pixels are classified into high-grayscale luminance pixels,of which pixel luminance is greater than the entire-grayscale luminanceaverage, and low-grayscale luminance pixels, of which the pixelluminance is less than the entire-grayscale luminance average; and theentire-grayscale luminance average is calculated as an average of thepixel luminance of all of the pixels, the low-grayscale luminanceaverage is calculated as an average of the pixel luminance of thelow-grayscale luminance pixels, and the high-grayscale luminance averageis calculated as an average of the pixel luminance of the high-grayscaleluminance pixels.
 6. The method of claim 5, wherein the block luminanceis calculated as an average of the pixel luminance of the pixelsincluded in each of the display blocks.
 7. The method of claim 5,wherein the block luminance is calculated as a weighted average of thepixel luminance of the pixels included in each of the display blocks. 8.The method of claim 5, wherein the block luminance is determined as aminimum grayscale among grayscales corresponding to the pixel luminanceof the pixels included in each of the display blocks.
 9. A method ofperforming an image-adaptive tone mapping, the method comprising:calculating an entire-grayscale luminance average, a low-grayscaleluminance average, and a high-grayscale luminance average of an imageframe to be displayed on a display panel by analyzing a data signalcorresponding to the image frame; determining a first tone mappingfunction to be applied to the image frame based on the entire-grayscaleluminance average, the low-grayscale luminance average, and thehigh-grayscale luminance average; dividing the display panel into aplurality of display blocks by grouping a plurality of pixels includedin the display panel by location; classifying the display blocks intonon-target display blocks, of which block luminance is greater than ablock luminance average of N adjacent display blocks, where N is aninteger greater than or equal to 8, and target display blocks, of whichthe block luminance is less than the block luminance average; performinga first tone mapping on the image frame by applying the first tonemapping function to each of the non-target display blocks; andperforming a second tone mapping on the image frame by applying a secondtone mapping function to each of the target display blocks, the secondtone mapping function being obtained by applying a local weighted valueto the first tone mapping function.
 10. The method of claim 9, whereinthe first tone mapping function is expressed by [Equation 1] below:OUTPUT1=GTM(INPUT),   [Equation 1] where GTM denotes the first tonemapping function, INPUT denotes a luminance signal which is extractedfrom the data signal, and OUTPUT1 denotes a first output luminancesignal which is obtained by performing the first tone mapping on theluminance signal.
 11. The method of claim 10, wherein the second tonemapping function is expressed by [Equation 2] below:OUTPUT2=(1+α)×GTM(INPUT),   [Equation 2] where GTM denotes the firsttone mapping function, INPUT denotes the luminance signal which isextracted from the data signal, a denotes the local weighted value, andOUTPUT2 denotes a second output luminance signal which is obtained byperforming the second tone mapping on the luminance signal.
 12. Themethod of claim 11, wherein: the local weighted value decreases within apredetermined weighted value range as a luminance ratio which iscalculated by dividing the block luminance of the each of the targetdisplay blocks by the block luminance average of the N adjacent displayblocks increases; and the local weighted value increases within thepredetermined weighted value range as the luminance ratio decreases. 13.The method of claim 9, wherein: the pixels are classified intohigh-grayscale luminance pixels, of which pixel luminance is greaterthan the entire-grayscale luminance average, and low-grayscale luminancepixels, of which the pixel luminance is less than the entire-grayscaleluminance average; and the entire-grayscale luminance average iscalculated as an average of the pixel luminance of all of the pixels,the low-grayscale luminance average is calculated as an average of thepixel luminance of the low-grayscale luminance pixels, and thehigh-grayscale luminance average is calculated as an average of thepixel luminance of the high-grayscale luminance pixels.
 14. The methodof claim 13, wherein the block luminance is calculated as an average ofthe pixel luminance of the pixels included in each of the displayblocks.
 15. The method of claim 13, wherein the block luminance iscalculated as a weighted average of the pixel luminance of the pixelsincluded in each of the display blocks.
 16. The method of claim 13,wherein the block luminance is determined as a minimum grayscale amonggrayscales corresponding to the pixel luminance of the pixels includedin each of the display blocks.
 17. A display device, comprising: adisplay panel comprising a plurality of pixels; and a display paneldriving circuit configured to drive the display panel, wherein thedisplay panel driving circuit calculates an entire-grayscale luminanceaverage, a low-grayscale luminance average, and a high-grayscaleluminance average of an image frame to be displayed on the display panelby analyzing a data signal corresponding to the image frame, determinesa first tone mapping function to be applied to the image frame based onthe entire-grayscale luminance average, the low-grayscale luminanceaverage, and the high-grayscale luminance average, divides the displaypanel into a plurality of display blocks by grouping the pixels bylocation, classifies the display blocks into non-target display blocksand target display blocks based on block luminance of each of thedisplay blocks, performs a first tone mapping on the image frame byapplying the first tone mapping function to each of the non-targetdisplay blocks, and performs a second tone mapping on the image frame byapplying a second tone mapping function to each of the target displayblocks, the second tone mapping function being obtained by applying alocal weighted value to the first tone mapping function.
 18. The displaydevice of claim 17, wherein the display panel driving circuit classifiesthe display blocks into the non-target display blocks, of which theblock luminance is greater than the low-grayscale luminance average, andthe target display blocks, of which the block luminance is less than thelow-grayscale luminance average.
 19. The display device of claim 17,wherein the display panel driving circuit classifies the display blocksinto the non-target display blocks, of which the block luminance isgreater than a block luminance average of N adjacent display blocks,where N is an integer greater than or equal to 8, and the target displayblocks, of which the block luminance is less than the block luminanceaverage.
 20. The display device of claim 17, wherein the first tonemapping function is expressed by [Equation 1] below:OUTPUT1=GTM(INPUT),   [Equation 1] where GTM denotes the first tonemapping function, INPUT denotes a luminance signal which is extractedfrom the data signal, and OUTPUT1 denotes a first output luminancesignal which is obtained by performing the first tone mapping on theluminance signal, and wherein the second tone mapping function isexpressed by [Equation 2] below:OUTPUT2=(1+α)×GTM(INPUT),   [Equation 2] where GTM denotes the firsttone mapping function, INPUT denotes the luminance signal which isextracted from the data signal, a denotes the local weighted value, andOUTPUT2 denotes a second output luminance signal which is obtained byperforming the second tone mapping on the luminance signal.